Use a template system (or an include system) that either runs server side (most common) or at build time (which can support HTTP servers which only allow static files).
Use whatever programming language you like (subject to support by your server if you are doing this server-side); PHP is as common as muck, Java is an option, I tend towards Perl (and more specifically: Template Toolkit), there are many others. JavaScript is becoming increasingly popular for this type of job, with tools such as assemble becoming available. You can go all the way with a static site generator.
Use a search engine to find popular template languages or include systems for your programming language of choice.
